An ultrasonic diagnostic apparatus transmits ultrasound to biological tissue in a subject by an ultrasonic probe. Echo signals of the ultrasound are received by the ultrasonic probe, and an ultrasonic image based on the echo signals is produced.
The ultrasonic probe comprises a plurality of ultrasonic vibrators. Transmission/reception of ultrasound is conducted in each of the plurality of ultrasonic vibrators. An echo signal received at each ultrasonic vibrator is input to a reception beamformer. The reception beamformer applies reception beamforming to the echo signal received at each ultrasonic vibrator. The reception beamforming is phased-addition processing involving delaying the echo signals received at the ultrasonic vibrators and adding the resulting signals together.
A delay time in the reception beamforming is defined assuming that the sound velocity of ultrasound in biological tissue has a given value. The value of the sound velocity of ultrasound in biological tissue, however, may sometimes vary from subject to subject or from region to region. Therefore, in case that the value of the sound velocity set for determining a delay time is different from an actual value of the sound velocity, a reception focus may be degraded.
Accordingly, Japanese Patent No. 3642607 discloses an ultrasonic tomography apparatus for determining a value of the sound velocity of ultrasound such that a variance of the spatial frequency for the amplitude of ultrasonic received signals is maximized, and correcting a value of the sound velocity of ultrasound set in the apparatus.